Within the field of wireless telecommunications systems, there exists a system referred to as the personal handy phone system, otherwise known as PHS. Within the personal handy phone system, a user of a portable or personal station (PS) device is capable of communicating with a user of another telecommunication device by way of a cell station (CS) device. Furthermore, the portable station within the personal handy phone system can also function as an answering machine by recording incoming voice/sound messages and then playing them back later at some desired time. Moreover, the portable station can also be equipped with the capability to record both sides of a conversation when it is being used to communicate with another telecommunication device.
In order for a manufacturer of portable stations to keep competitively priced within a commercial market, it is important for the manufacturer to minimize its manufacturing costs of the portable stations. There are several different ways to decrease the cost of manufacturing portable stations, which include utilizing less expensive components to produce the same functionality. Another way to decrease manufacturing costs is to limit the amount of integrated circuit chips (e.g., memory chips) installed within the portable stations to some minimum requirement. By utilizing the above mentioned techniques along with others, the manufactured portable stations are competitively priced when sold to the general public.
Since the amount of memory space within a portable station is limited, it is important to maximize the usage of available memory resources as much as possible. In order to maximize the usage of available memory space, it is important to focus on portable station functions that utilize a large amount of memory space. For instance, one memory demanding function performed by the portable station is the recording of received voice and sound signals. There are several prior art methods within the personal handy phone system to maximize memory space usage while a portable station is recording voice/sound signals. One prior art method is to store the received voice/sound signals in memory using the compressed data format in which they are received by the portable station, e.g., a full rate (32 kilobits-per-second) 4-bit adaptive differential pulse code modulation (ADPCM) compressed data format. The problem associated with this prior art solution is that the voice/sound signals in the full rate 4-bit ADPCM compressed data format occupy too much of the memory space located within the portable station.
Another prior art method to maximize the limited memory space contained within a portable station when it is functioning as a voice recorder is to use a digital signal processor (DSP) integrated circuit chip within the portable station to further compress the received voice/sound signals before storing them within memory. The problem associated with this prior art solution is that digital signal processor integrated circuit chips are very expensive components, which dramatically increase the manufacturing cost of a portable station. As described above, phone manufacturers desire to reduce the expense of the portable stations to remain competitive in this market.
Therefore, it would be advantageous to provide a cost effective system enabling a portable station within the personal handy phone system to record voice and sound signals while increasing its usage of its available memory space and subsequently playing the recorded messages back. The present invention provides these advantages.